A direct measure of positive feedback loop-gain due to reverse bias damage in thin-film solar cells using lock-in thermography

In this work, we present a method to study thermal runaway effects in thin-film solar cells. Partial shading of solar cells often leads to permanent damage to shaded cells and degrades the performance of solar modules over time. Under partial shading, the shaded cells may experience a reverse bias junction breakdown. In large-area devices such as solar cells, this junction breakdown tends to take place very locally, thus leading to very local heating and so-called “hot-spots”. Previously, it was shown that a positive feedback effect exists in Cu(In,Ga)Se2 (CIGS) thin-film solar cells, where a highly localized power dissipation is amplified, which may lead to an unstable thermal runaway process. Furthermore, we introduced a novel characterization technique, laser induced Hot-Spot Lock-In Thermography (HS-LIT), which visualizes the positive feedback effect. In this paper, we present a modified HS-LIT technique that allows us to quantify directly a loop-gain for hot-spot formation. By quantifying the loop-gain we obtain a direct measure of how unstable a local hot-spot is, which allows the non-destructive study of hot-spot formation under various conditions and in various cells and cell types. We discuss the modified HS-LIT setup for the direct measurement of the loop-gain. Furthermore, we demonstrate the new method by measuring the loop-gain of the thermal runaway effect in a CIGS solar cell as a function of reverse bias voltage

Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

For indoor light harvesting, the adjustable band gap of molecular semiconductors is a significant advantage relative to many inorganic photovoltaic technologies. However, several challenges have to be overcome that include processability in nonhalogenated solvents, sufficiently high thicknesses (>250 nm) and high efficiencies at illuminances typically found in indoor environments. Here, we report on the development and application of new methods to quantify and identify performance losses based on thickness- and intensity-dependent current density–voltage measurements. Furthermore, we report on the fabrication of solar cells based on the blend PBDB-T:F-M processed in the nonhalogenated solvent o-xylene. In the low-intensity regime, insufficiently high shunt resistances limit the photovoltaic performance and by analyzing current density voltage–curves for solar cells with various shunt resistances we find that ∼100 kΩ cm2 are required at 200 lux. We provide a unified description of fill factor losses introducing the concept of light-intensity-dependent apparent shunts that originate from incomplete and voltage-dependent charge collection. In experiment and simulation, we show that good fill factors are associated with a photo-shunt inversely scaling with intensity. Intensity regions with photo-shunt resistances close to the dark-shunt resistance are accompanied by severe extraction losses. To better analyze recombination, we perform a careful analysis of the light intensity and thickness dependence of the open-circuit voltage and prove that trap-assisted recombination dominates the recombination losses at low light intensities

Impact of Laser Treatment on Hydrogenated Amorphous Silicon Properties

Herein, the application of laser radiation to locally modify the hydrogen distribution within hydrogenated amorphous silicon films on a short time scale is studied. The impact of laser power and irradiation time on the temperature of the silicon layer during the laser treatment and the hydrogen outdiffusion is analyzed. Moreover, the resulting optoelectronic properties of the amorphous silicon are examined. On a timescale of a few seconds or less, the hydrogen concentration in the near‐surface region of the silicon layer can be successfully decreased without major impact on the optoelectronic properties

data and code for paper "Shallow Defects and Variable Photoluminescence Decay Times up to 280 µs in Triple-Cation Perovskites"

<p>data of the figures shown in main text and in the supporting information, as well as MATLAB scripts for steady-state and transient photoluminescence simulations in the paper "Shallow Defects and Variable Photoluminescence Decay Times up to 280 µs in Triple-Cation Perovskites".</p&gt

A unified description of non-radiative voltage losses in organic solar cells

Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (ΔVnr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of ΔVnr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-ΔVnr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of ΔVnr. We also demonstrate that the reduction in ΔVnr (for example, <0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region

Theorie und Praxis der Unternehmerfamilie und des Familienunternehmens – Theory and Practice of Business Families and Family Businesses

Dieser Band ist die Festschrift für Prof. Dr. Arist von Schlippe zu seinem 70. Geburtstag im April 2021. Der Jubilar hat im Rahmen seiner Tätigkeit am Wittener Institut für Familienunternehmen (WIFU) an der Universität Witten/Herdecke seit 2005 eine besondere Wirkung in der Forschung und im Praxistransfer entfaltet. Langjährige Forscherkolleg*innen, Wegbegleiter*innen, Freunde und Freundinnen ehren mit diesem Band die große Leistung von Arist von Schlippe und zeigen auf, welche Spuren er in 15 Jahren in diesem Feld hinterlassen hat. Arist von Schlippe ist in der Gemeinde der Familienunternehmensforscher*innen weithin bekannt, fachlich anerkannt und respektiert, aber mehr noch: Er wird als Mensch sehr geschätzt. Knapp 40 nationale und internationale Kolleg*innen aus der Forschung, der Beratung und dem Feld des Familienunternehmertums widmen ihm Fachbeiträge zu zentralen Fragestellungen im Umfeld ihrer Arbeit. Die Beiträge zum Wirken des Geehrten tragen eine je persönliche Note